The present invention relates to an illumination system for use with machine vision systems, such as optical and barcode scanning systems. More particularly, it relates to a system for strobing a light source in sync with a camera shutter or other machine vision system; such that the camera shutter is open or the machine vision system is activated when the light source is on.
There are various lighting technologies used in traditional machine vision systems. While the choice of lighting largely depends on the type of image enhancement required (i.e diffusion, feature enhancement, profile), high speed image capture requires sufficient light energy for use with very short exposure times. Depending on image exposure requirements, different light sources can be used, each having its advantages and disadvantages.
For a long exposure time, such as greater than 1 ms, a system might use fluorescent or LED lighting. Such systems are advantageous because they consume less power and dissipate heat efficiently. The disadvantage of such systems are that low light output limits use to long exposures, and therefore slow speed imaging. Further, they are vulnerable to ambient light, and requires either shielding to limit external light or an optical filter to pass only monochromatic light.
For a shorter exposure time, such as that less than 1 ms, but not using a strobed light source, a system might use halogen, high pressure sodium, or metal halide lighting. The advantages for of such lighting systems are the high light output that is useful in high speed imaging. The disadvantages are low efficiency because the system consume a lot of power and dissipate heat. Further, the bright light source can be an annoyance to nearby personnel, and light shields are sometimes required to limit exposure to personnel.
For a shorter exposure time, such as that less than 1 ms, using a strobed light source, a system might use LEDs (which can be strobed at many times rated DC current value, yielding much higher light output; see applicant's examples below) or Xenon lighting. The advantages of such lighting systems are the high light output for use in high speed imaging combined with high efficiency because of low power consumption and heat dissipation. The disadvantage is that the strobing source can be annoying to nearby personnel. Frequencies of 7 HZ-15 HZ are particularly dangerous since they have been shown to trigger epileptic seizures. Further, light shields are sometimes required to limit exposure to personnel.
In order to increase accuracy and maintain consistency in the data collected by machine vision systems, it is important to have an efficient direct source of light to fully illuminate the area being scanned (hereinafter the “illumination area”). The invention seeks to solve this problem and overcome the problems of the prior art.